A basis for mapping the erodibility of tidal flats by optical remote sensing

A means of monitoring surface sediment stability of tidal flats with optical remote sensing has been developed. Erosion shear stress and corresponding bio-geo-chemical parameters of tidal flats were measured over five years in the Sylt/Rømø Bight, Germany. Ground-based optical reflectance spectra were measured during one year. A significant dependence of erosion shear stress on the benthic diatom chlorophyll a concentration in the uppermost 1-mm layer was found for muddy areas but decreased with decreasing proportion of fine particles (< 63 µm). With a low phytobenthic coverage there was a weak dependence of erosion shear stress on the proportion of fine particles. There were two main classes of the reflectance spectra: containing information on sediment type i.e. proportion of fine particles, and containing information on benthic diatoms and other phytobenthic species. There was a significant correlation between the reflectance spectra and proportion of fine particles and also between reflectance spectra and benthic diatom chlorophyll α concentration. Hence, the erodibility of tidal flats can be mapped by optical remote sensing when benthic chlorophyll a concentration and proportion of fine particles are used for estimation of the erosion shear stress.